Global NMR Discussion Meetings

Quantum Sensing

  • Slow Water in Engineered Nanochannels Revealed by Color-Center-Enabled Sensing

    Rohma Khan (CUNY City College of New York, CUNY Graduate Center, United States)

    Bluesky: @gbalavoi.bsky.social‬

    Abstract: Characterization of nanoscale confinement of liquids via quantum sensing can overcome the sensitivity, spatial, and temporal limitations of other measurement techniques, allowing deeper understanding of dynamics central to areas spanning geophysics, tribology, catalysis, polymer science, and biology. Using shallow nitrogen vacancy (NV) centers as our quantum sensors we probe the molecular dynamics of water molecules confined within engineered ~5-nm-tall channels formed by a hexagonal boron nitride (hBN) structure on the diamond surface. Our resultant NV-enabled nuclear magnetic resonance spectra of confined water protons reveal a reduced H2O self-diffusivity, orders of magnitude lower than that in bulk water. Correlation measurements show us long lasting nuclear spin coherences, indicative of molecular dynamics intermediate between bulk water and ice. Molecular dynamics modeling indicate cluster formations may arise from accumulation of surface charge and carrier injection into the fluid under laser illumination. Our next step is the extension of these experiments to variable temperatures with preliminary findings showing narrowing of our NV NMR Spectra as we approach freezing point.

    1. Yunfan Qiu Avatar
      Yunfan Qiu

      Hi Rohma,
      Excellent presentation. From the perspective of an organic chemist, I am curious if you could use the same system to detect protons in other solvents, such as organic solvents instead of water. Would you expect to observe different proton frequencies depending on the chemical structure of the solvents, and achieve NV-enabled H NMR? Thanks!

      Reply
    2. Rohma Khan Avatar
      Rohma Khan

      Hello Yunfan Qiu,

      Thank you for your question!

      We can use the same system to detect protons in other solvents, in my colleague’s case he is able to detect protons in fluorinated oil. We have also tried this with PEG. In our system we would not be able to observe different proton frequencies depending on the chemical structure of the solvents, but others have with a slightly modified setup. Here is the citation for them Glenn, D., Bucher, D., Lee, J. et al. High-resolution magnetic resonance spectroscopy using a solid-state spin sensor. Nature 555, 351–354 (2018). https://doi.org/10.1038/nature25781

      One of the key points in our system is that we work with statistical polarization but to see the chemical shifts we need thermally polarized nuclear spins. Please let me know if you have any further questions, thanks!

      Rohma

      Reply
    3. Raj Chaklashiya Avatar
      Raj Chaklashiya

      Hi Rohma, interesting presentation! I am wondering if there are good ways to optimize this technique without substantially changing the result. I am thinking of two ways:
      1) Optimizing the diamond properties (e.g. number of NV centers, closeness of NV centers to the surface, size of the diamond, etc.)
      2) Implementing Dynamic Nuclear Polarization via organic radicals being placed in the solvent and microwaves being shined onto the water to enhance the NV-NMR signal
      I am curious about your thoughts on these two and whether you already know ways the diamond could be optimized or how compatible DNP could be with your methodology (would the radicals interfere too much with the end result?)
      Thank you!

      Reply

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  • Optically Addressable NV Centers for Quantum Sensing

    Amaria Javed (NYU Abu Dhabi, United Arab Emirates)

    Abstract: This talk presents our ongoing work on NV-diamond-based quantum sensing at the Center for Quantum and Topological Systems (CQTS) at NYU Abu Dhabi, with a focus on optical techniques for spin state readout and signal enhancement. Nitrogen-Vacancy (NV) centers in diamond are point defects that serve as atomic-scale quantum sensors, offering remarkable sensitivity to magnetic and electric fields, temperature, and strain. These color centers exhibit spin-dependent fluorescence under green laser excitation, enabling optical initialization and readout of their quantum state even at room temperature.
    At the core of our experimental approach is Optically Detected Magnetic Resonance (ODMR), a technique that uses changes in NV center fluorescence to measure shifts in spin transitions, revealing information about the surrounding environment. We are currently building a custom NV-based sensing setup, which involves laser excitation at 532 nm, microwave control of spin transitions, and efficient fluorescence detection via optical filters and photodetectors.
    Our work aims to optimize the optical alignment, fluorescence collection efficiency, and stability of the system for robust quantum sensing applications. We explore methods to enhance contrast in ODMR spectra, increase sensitivity, and suppress background noise, which are critical for real-time, high-resolution measurements. These efforts lay the foundation for emerging applications in nanoscale magnetometry, bioimaging, materials characterization, and lab-on-a-chip sensing technologies.
    This presentation will give an overview of the NV center’s optical properties, practical design considerations in setting up an ODMR experiment, and the broader role of photonics in quantum sensing.

    1. Yunfan Qiu Avatar
      Yunfan Qiu

      Hi Amaria,
      Thank you for your presentation. What specific object or system do you plan to detect using the NV center through ODMR? I assume it is something spin active, so it can interact with the NV and cause observable changes in the emission? Looking forward to hearing more about your project.

      Reply
    2. Amaria Javed Avatar
      Amaria Javed

      Thank you for your interest! Yes, you’re absolutely right, the NV center is sensitive to spin-active species. In our project, we are focusing on EPR detection using the NV center, specifically targeting unpaired electron spins in external samples. The idea is to use the NV’s spin-dependent photoluminescence and ODMR contrast to detect and characterize these spins at the nanoscale.

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  • Probing interfacial water via color-center-enabled spin magnetometry

    Kang Xu (CUNY–The City College of New York, United States)

    LinkedIn: @Kang Xu‬

    Abstract: We use shallow nitrogen-vacancy (NV) centers in diamond to probe the nanoscale dynamics of interfacial water confined between diamond and a fluorinated oil layer. By selectively detecting 1H and 19F nuclei using NV-NMR, we resolve distinct diffusion behaviors of water and oil near the interface. Our results reveal that water diffuses much faster than oil and is gradually displaced over days. Molecular dynamics simulations and surface-sensitive X-ray spectroscopy support the observation of slow, thermally driven reorganization. This work highlights NV-NMR as a powerful tool for studying molecular-scale interfacial processes under ambient conditions.

    1. Yunfan Qiu Avatar
      Yunfan Qiu

      Hi Kang,
      Exciting experiments and results! Regarding the H signal with a broad linewidth of 70 kHz, do you have any thoughts on how to achieve a narrower signal with better resolution? Looking forward to hearing your insights.

      Reply
    2. Kang Avatar
      Kang

      Hi Yunfan,

      Thanks for your comment! The 70 KHz signal is FFT result from correlation measurement protocol. Which is FID like signal resulted from diffusion out the detection zone of NV. Narrower linewidth could be down by deeper NV for micrometer scale detectio or hyperpolarize the target nuclei to overcome the thermal polarization limit. However, I don’t think these two approach would work for H signal from interfacial water. Firstly, micrometer scale detection may not gain more signal from thin interfacial water; secondly, hyperpolarize interfacial water maybe not that easy? Thanks for your comment agian!

      Reply
    3. Raj Chaklashiya Avatar
      Raj Chaklashiya

      Hi Kang,
      Nice presentation! One thing I am confused about is, why do 19F and 1H have these differing behaviors around the diamond? Is it only because 19F is more “slow” or are there other factors involved?

      Reply
      1. Kang Avatar
        Kang

        Hi Raj,

        Thanks for your comment! I think “slow” should be the main factor of there diffusion behavior. But the two dimensional nature of 2D of 1H and 3D nature of 19F may also cause some difference, althrough we did not go very detail about this difference. There is a paper considering this model as a difference. “Power-law scaling of correlations in statistically polarised nano-NMR”. Have a nice weekend!

        Best
        Kang

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  • Dynamic Nuclear Polarization Mechanisms in Diamond Defect Systems: Analytical Models and Transfer Dynamics

    Shubham Kumar Debdatta (Indian Institute of Science, Bangalore, India)

    Abstract: Nitrogen-vacancy (NV) centers in diamond have become prominent platforms for dynamic nuclear polarization (DNP), offering a robust route to hyperpolarize surrounding ¹³C nuclear spins under ambient conditions. Experimental observations have revealed both microwave-assisted and microwave-independent DNP pathways, frequently rationalized in terms of level anti-crossings between coupled electronic and nuclear spin manifolds.
    In this work, we construct an analytical treatment of spin polarization transfer from NV centers to proximal ¹³C nuclei, employing the density matrix formalism in conjunction with average Hamiltonian theory. Under the condition of selective excitation of a single electronic transition, we invoke a reduced Hilbert space description to derive compact expressions for spin polarization resonance conditions, effective spin Hamiltonians, and transfer efficiency as a function of external magnetic field, hyperfine interaction strength, and applied microwave fields.
    The model is further generalized to incorporate NV–P1–¹³C configurations, where P1 centers—substitutional nitrogen defects with spin-½—mediate cross-relaxation pathways that enable microwave-free spin polarization transfer. This extension elucidates key dynamical features such as field-dependent polarization oscillations, resonance-enhanced transfer channels, and timescales associated with transient spin exchange processes.
    This theoretical framework offers a detailed understanding of DNP mechanisms across both isolated and interacting defect configurations. The results delineate optimal regimes for maximizing nuclear spin polarization in diamond-based systems, particularly under low magnetic fields and ambient conditions, with direct implications for enhancing the sensitivity of nuclear magnetic resonance (NMR) and other hyperpolarization-enabled techniques.

    1. Arianna Actis Avatar
      Arianna Actis

      Dear Shubham, thank you for the presentation, it is a very interesting study. If I understand correctly, the graph showing “Normalized Signal vs Time” shows the the polarization buildup on 13C. Could you comment on the factors that affect this polarization transfer? Thank you.

      Reply
    2. Shubham Kumar Debadatta Avatar
      Shubham Kumar Debadatta

      Thank you! I assume you’re referring to the NV–P1–13C cluster-based study. In this context, the transfer rate mostly depends on A_zz^Δ and A_zx^Δ, which represent the differences in secular and pseudo-secular hyperfine couplings. These differences are key factors governing the transfer rate.
      In the plot, the purple plot indicates no spin polarization transfer. This occurs when the 13C nuclear spin is positioned exactly midway between the NV center and the P1 center, resulting in zero difference in both secular and pseudo-secular hyperfine couplings—hence, no transfer takes place.
      Additionally, there is a dependence on θ (theta) and φ (phi), which are related to nuclear and electronic couplings. These angular dependencies reflect how spin polarization transfer is influenced by the relative positioning of the 13C nucleus—whether it’s closer to the NV or the P1 center—and by the physical distance between NV and P1.

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    3. Sajith V Sadasivan Avatar
      Sajith V Sadasivan

      Nice work, Shubham.

      Have you explored the simulations under MAS?

      Reply
    4. Shubham Kumar Debadatta Avatar
      Shubham Kumar Debadatta

      Thank you! I haven’t looked into the matching conditions under MAS yet.

      Reply
      1. Sajith V Sadasivan Avatar
        Sajith V Sadasivan

        Okay.

        Reply
    5. Arianna Actis Avatar
      Arianna Actis

      Hello Shubham, thank you for your answer. Did you try also to study clusters composed by multiple NV and P1 centres?

      Reply
    6. Shubham Kumar Debadatta Avatar
      Shubham Kumar Debadatta

      Yes, I am currently exploring cluster-based systems. At the moment, our primary focus is on the 14N nucleus (associated with the P1 center) within the NV–P1–13C spin system, examining its dynamics as a four-spin system.

      Reply
    7. Raj Chaklashiya Avatar
      Raj Chaklashiya

      Dear Shubham,
      Nice presentation! I was wondering, while your simulations show that the optimal matching conditions are at X Band, is there any way that you’ve seen to manipulate the spin system (e.g. via couplings) such that the optimal matching condition can occur at higher field? Like basically–what about the system would have to be changed for the optimal condition to be at high field?

      Reply
    8. Shubham Kumar Debadatta Avatar
      Shubham Kumar Debadatta

      Hi Raj, Thank you! I believe I may not be fully understanding your question. The matching conditions remain the same and are highly valid in the high-field regime. However, as the magnetic field strength increases, the range over which spin polarization transfer occurs becomes narrower. This is because, at higher fields, the matching condition primarily depends on the nuclear Larmor frequency, with much less influence from hyperfine couplings. This trend is also demonstrated in the presentation at 9.4 Tesla.

      Reply
      1. Raj Chaklashiya Avatar
        Raj Chaklashiya

        Thanks! That makes sense to me–so it would have to require tuning the nuclear larmor frequency for it to work well at high fields.

        Reply

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